1. Field of the Invention
The present invention relates to a color cathode ray tube which displays a color image, and more particularly to a color cathode ray tube having a deflection unit of an improved structure.
2. Description of the Related Art
A color cathode ray tube which is used as a color television picture tube, a monitor tube of an information equipment or the like is constituted of a vacuum envelope which is formed by connecting a panel portion having a phosphor screen (also simply referred to as xe2x80x9cscreenxe2x80x9d) on an inner surface thereof and a neck portion which accommodates an electron gun for irradiating electron beams by means of a funnel portion.
In the color cathode ray tube having such a vacuum envelope, to obtain the best convergence under the favorable focusing characteristic over the whole region of a phosphor screen which constitutes a display screen thereby obtaining the high resolution without color irregularities, a magnet assembly which is constituted of magnets having a plurality of magnetic poles is arranged on an outer surface of the neck portion which accommodates the electron gun and the loci of electric beams are corrected by the magnetic field.
Further, the color cathode ray tube includes horizontal and vertical deflection coils for performing the deflection scanning of electron beams irradiated from the electron gun in the horizontal direction as well as in the vertical direction. Further, the color cathode ray tube exteriorly mounts a deflection unit which includes a rotation correction coil which corrects the rotation of an image (raster) on the screen and a magnetic current modulator (MCM) which corrects raster distortions, that is, a so-called inner pin at a central region of the screen on a boundary between the neck portion and the funnel portion.
FIG. 8 is a side cross-sectional view for schematically explaining a structural example of a color cathode ray tube which mounts a deflection unit on a color cathode ray tube. The color cathode ray tube is formed of a vacuum envelope which is constituted of a panel portion 1 having a phosphor screen 4, a neck portion 2 and a funnel portion (also referred to as xe2x80x9ccone portionxe2x80x9d) 3 which contiguously connects the panel portion 1 and the neck portion 2. The color cathode ray tube is also configured such that a deflection unit 15 which includes a deflection yoke 16 is exteriorly mounted over a transitional region from the neck portion 2 to the funnel portion 3.
An electron gun 11 which irradiates three electron beams B are housed in the inside of the neck portion 2, the phosphor screen 4 which is formed on an inner surface of the panel portion 1 includes three-colored phosphors coated thereon in a mosaic form, and a shadow mask structural body 5 which constitutes a color selection electrode is arranged in the vicinity of the phosphor screen 4.
The shadow mask structural body 5 includes a support frame 7 which holds a shadow mask 6 and is held by engaging suspension springs 8 with stud pins 9 which are mounted in an erected manner on an inner wall of a skirt portion of the panel portion 1. Further, a magnetic shield 10 which shields an external magnetic field is mounted on an electron-gun side of the shadow mask structural body 5 Here, an implosion prevention band 14 is fastened to an outer-side wall of the panel portion 1.
FIG. 9 is enlarged side view of the deflection unit 15 which is exteriorly mounted on the color cathode ray tube. An arrow P side of the deflection yoke 16 incorporated into the deflection unit 15 is a large-diameter portion which constitutes a phosphor screen side and an arrow G side is a small-diameter portion which constitutes an electron-gun side and exhibits an approximately funnel shape. A horizontal deflection coil is disposed in the inside of the deflection yoke 16 and the vertical deflection coil is disposed in the outside of the deflection yoke 16 by way of a separator. Further, a core made of ferrite or the like is disposed in the outside of the vertical deflection coil.
Further, a rotation correction coil 17 is mounted on the large-diameter-portion-side end portion of the deflection yoke 16, while a magnet assembly 12 which is formed by combining magnets of 4 poles or 6 poles is mounted on the small-diameter-portion side of the deflection yoke 16.
An upper protective cover 19 which houses a convergence adjusting circuit board 18 is provided to a top portion (upper side in FIG. 9) of the deflection unit 16, while a lower protective cover 21 which houses a circuit board on which a magnetic current modulator (MCM) 20 is mounted is provided to a bottom portion (lower side in FIG. 9) of the deflection unit
Further, a fixing band 22 is provided to the small-diameter-portion side of the deflection yoke 16 which constitutes the electron-gun side and the fixing band 22 is fixedly secured to the neck portion 2 by fastening. The whole deflection unit 15 is tilted using the fixing point as a fulcrum to adjust the deflection unit 15 to the best position and, thereafter, the deflection unit 16 is mounted on a portion ranging from the funnel portion 3 to the neck portion 2 by inserting a plurality of wedges between the large-diameter-portion side and the funnel portion 3.
Here, in FIG. 9, numeral 23 indicates a power supply line for supplying electricity to the rotation correction coil 17 and numeral 24 indicates a power supply line for supplying electricity to deflection coils.
FIG. 10 is a plan view for explaining a constitutional example of the magnetic current modulator 20. The magnetic current modulator 20 is served for correcting the pin distortions at a central region of a screen of the cathode ray tube and is constituted of modulation coils which are respectively inserted into a vertical deflection coil and a horizontal deflection coil in series and a bias magnet.
In FIG. 10, numeral 202 indicates a vertical modulation coil and numerals 203 and 204 indicate horizontal modulation coils. A structure in which the horizontal modulation coils 203 and 204 are arranged at both sides of the vertical modulation coil 202 and these modulation coils 203, 204 are sandwiched by bias magnets 205, 206 from both sides is housed in the inside of a resin casing 201 and is mounted on a printed circuit board which will be explained later. Here, respective coils are wound around magnetic cores and an adhesive agent 208 is coated over each portion defined between cores of the neighboring coils and bias magnets 205, 206 which are arranged close to the cores so as to fix them together.
FIG. 11 is a developed view for explaining the arrangement of the coils and bias magnets of the magnetic current modulator. The vertical modulation coil 202 is constituted of a vertical modulation coil 202b which is wound around one vertical core 202a and the horizontal modulation coils 203, 204 are constituted of horizontal modulation coils 203b, 203d, 204b, 204d which are respectively wound around respective pairs of horizontal cores 203a, 203c, 204a, 204c which are arranged in parallel.
At both ends in the winding axis direction of the vertical modulation coil 202, the winding axis directions of the horizontal modulation coils 203, 204 are arranged in parallel and the bias magnets 205, 206 are arranged at the outermost side of the horizontal modulation coils 203, 204.
The winding axis directions of the vertical modulation coil 202 and respective horizontal modulation coils 203, 204 are set to directions which generate magnetic fields indicated by arrows in the drawing and these modulation coils are inserted between the vertical deflection coil and the horizontal deflection coil in series so as to correct the inner pin distortions of the raster on the screen.
FIG. 12 is a plan view for explaining a mounting state of the magnetic current modulator 20 on a printed circuit board 207. The magnetic current modulator 20 is mounted on the printed circuit board 207 in place. The printed circuit board 207 and the magnetic current modulator 20 are fixedly secured to each other using an adhesive agent 209. Here, the resin casing 201 of the magnetic current modulator 20 and the printed circuit board 207 may be fixedly secured to each other using stopper means or other known fixing means such as caulking or screwing together with the adhesive agent 209.
As a literature which discloses a related art relevant to this type of cathode ray tube, Japanese Laid-open Patent Publication 268746/2000 can be named, for example.
In the cathode ray tube using the magnetic current modulator having such a constitution, during the operation, the vertical or horizontal cores 202a, 203a, 203c, 204a, 204c or the bias magnets 205, 206 which constitute the magnetic current modulator 20 generate the magnetic distortion due to the magnetic fields generated by respective coils. Accordingly, there have been cases in which the mechanical vibrations caused by these magnetic distortions impinge on the neighboring vertical and horizontal cores, bias magnets or the resin casing so that an uncomfortable sound, so-called xe2x80x9csingingxe2x80x9d is generated.
This uncomfortable sound constitutes a xe2x80x9cbeating soundxe2x80x9d having high frequency of a specified horizontal frequency which flows in the deflection yoke, for example, approximately 15 kHz in the vicinity of 69 kHz,. There is a possibility that such an uncomfortable sound is generated at a band of other frequencies in the similar manner. Such an uncomfortable sound brings about the poor evaluation of the quality of a monitor or a picture receiving set which incorporates the cathode ray tube therein.
The present invention provides a cathode ray tube of high quality by preventing the occurrence of an uncomfortable sound derived from a magnetic current modulator in the cathode ray tube.
According to the present invention, a clamp unit which brings respective vertical and horizontal cores and the bias magnets of a magnetic current modulator into close contact with each other in the arrangement direction (axial direction) of the respective cores is disposed in a resin casing of the magnetic current modulator.
The clamp unit uses a resilient body which is made of non-magnetic material such as stainless steel and is preferably formed of non-magnetic metal, wherein the above-mentioned respective cores and bias magnets are brought into pressure contact with each other from the outside of the resin casing by means of a resilient body in the axial direction of the vertical and horizontal cores.
Due to such a constitution, the generation of an uncomfortable sound derived from the magnetic distortion of the vertical and horizontal cores or the bias magnets which constitute the magnetic current modulator can be prevented so that the quality of a monitor or a picture receiving set which incorporates a cathode ray tube therein can be enhanced.
Further, by coating an adhesive agent on a portion between the neighboring respective vertical and horizontal cores and a portion between these cores and the bias magnets disposed close to the vertical and horizontal cores, the generation of the uncomfortable sound can be prevented more effectively.